Here is my code so far:
import arcpy
from arcpy.sa import *
arcpy.CheckOutExtension("Spatial")
workspace = arcpy.env.workspace = "C:/Users/KJanus/Desktop/Intro_ArcGIS/RasterData_Lab6"
arcpy.CreateFolder_management(workspace, "NDVI")
arcpy.env.overwriteOutput = True
RED_1 = arcpy.Raster("C:/Users/KJanus/Desktop/Intro_ArcGIS/RasterData_Lab6/landtm1.img/Layer_3")
NIR_1 = arcpy.Raster("C:/Users/KJanus/Desktop/Intro_ArcGIS/RasterData_Lab6/landtm1.img/Layer_4")
RED_2 = arcpy.Raster("C:/Users/KJanus/Desktop/Intro_ArcGIS/RasterData_Lab6/landtm2.img/Layer_3")
NIR_2 = arcpy.Raster("C:/Users/KJanus/Desktop/Intro_ArcGIS/RasterData_Lab6/landtm2.img/Layer_4")
RED_3 = arcpy.Raster("C:/Users/KJanus/Desktop/Intro_ArcGIS/RasterData_Lab6/landtm3.img/Layer_3")
NIR_3 = arcpy.Raster("C:/Users/KJanus/Desktop/Intro_ArcGIS/RasterData_Lab6/landtm3.img/Layer_4")
print "Program recognizes raster bands."
NDVI_1 = (NIR_1 - RED_1)/(NIR_1 + RED_1)
sr = arcpy.sa.Con(RED_1<>0, NDVI_1, -9999)
NDVI_2 = (NIR_2 - RED_2)/(NIR_2 + RED_2)
sr = arcpy.sa.Con(RED_2<>0, NDVI_2, -9999)
NDVI_3 = (NIR_3 - RED_3)/(NIR_3 + RED_3)
sr = arcpy.sa.Con(RED_3<>0, NDVI_3, -9999)
print "NDVIs passed"
arcpy.CopyRaster_management("NDVI_1", "C:/Users/KJanus/Desktop/Intro_ArcGIS/RasterData_Lab6/NDVI",
format= "TIFF")
When I run the code I get these two errors: ExecuteError: Failed to execute. Parameters are not valid. ERROR 000732: Input Raster: Dataset NDVI_1 does not exist or is not supported